The present invention relates to a method and an apparatus for inspecting a single crystal ingot by means of the X-ray diffractometry to detect the direction of a crystallographic axis so as to determine the direction for an orientation flat (hereinafter merely referred to as "OF") to be made in the side of the single crystal ingot.
A semiconductor wafer to be made into substrates for semiconductor electronic devices is brought into being in the following manner: a single crystal ingot of a semiconductor material such as silicon is produced by means of a single crystal growing method such as the Czochralski (CZ) method; the ingot is then machined into a cylindrical form, and it is sliced into thin plates by cutting it in a direction substantially normal to the axis of the cylinder; next, the thin plates are lapped, etched and polished and eventually they become thin round disks having a mirror face on one side of them. Now, the thus made semiconductor wafers would be completely circular and have no visual clue to indicate any crystallographic orientation. For this reason, before being sliced into thin disks, the single crystal ingot is machined to have an orientation flat, which is a flat surface made in the side of the single crystal ingot in a manner such that the flat is normal to a crystallographic axis; the OF thus formed facilitates stage positioning of the resulting wafers, e.g., at the stage where optical pattern is given. Also, in some cases more than one orientation flat is made in a single crystal cylinder.
Naturally, a high precision is required in determining the direction of the OF to be made, and conventionally the crystallographic axes have been detected by means of the X-ray diffractometry (ref. Japanese Patent Application Kokoku No. 62-116243, for example).